The mechanism of action of various insecticides on the nerve and muscle will be studied by means of electrophysiological techniques. The structure-activity relationship of DDT and its derivatives will be analyzed by comparison of the effects on membrane ionic conductances. Our finding that aldrin-transdiol has a potent nerve blocking action gives promise of further development along this line, and detailed ionic mechanism of action will be elucidated. The effects of allethrin on ionic conductances have been worked out, but its site of action in the nerve membrane remains to be seen. This will be studied using internally perfused axons. The results of these studies are expected to provide us with the basis of improving existing insecticides and of developing new insecticides.